[jiggy2011]

Depends if you mean a programmer who is average relative to the rest of the team or a programmer who is average relative to all programmers but who is on a team of significantly better than average (therefor bad by the standard of the team).

A programmer who is worse than everyone else will tend to produce bugs that they themselves can't fix and also make poor design decisions. Both of these things will make things harder for the rest of the team.

In my experience there's a lot more bad programmers who produce lots of buggy code than produce low quantities of good quality code.